1. Field of the Invention
The invention relates to a pumping device for fluids, especially low-viscosity fluids such as washing suds or rinsing water. Such a device usually comprises a pump impeller, whose flexible vanes rotate in an annular pump chamber, and an electrical drive motor.
For fluid pumping a multitude of pumping devices are known. A pump impeller provided with vanes is rotated in a pump chamber by a drive shaft. Between the vanes and the pump chamber wall pumping compartments are formed in which the fluid which has entered the individual pumping compartments is accelerated and forced into a discharge connection.
2. Description of the Prior Art
Known pumps are usually driven by means of asynchronous motors which are commercially available at a low price, but which have a very poor efficiency. The poor efficiency makes it necessary to provide adequate cooling for the machine. Thus, pumping devices for fluids are generally substantially expensive and bulky. In the case of tight mounting conditions especially the large volumes of the units present problems.
It is known from the book "Centrifugal Pumps" by I. J. Karassik, pages 275 to 314) to drive pumps with single-phase synchronous motors. However, for dependable operation starting aids such as auxiliary windings and rotor cages are employed. Such starting aids are expensive.
It is also known (U.S. Pat. No. 1,402,719) to make the pump vanes flexible as so as to avoid jamming due to objects catching between the vanes and the pump chamber wall.